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What is tetany?

The action potential of skeletal muscle has a sharp rise and fall, as does an axon action potential. Thus rapid, successive discharges of a skeletal muscle fiber can result in tetany, which is the cumulation of multiple sustained contractions with no significant relaxation.

TRUE. They have as well a more prolonged action potential and plateau, and are more dependent upon calcium ion influx than are cardiac cells.

parasympathetic innervation of the ventricles is minimal, whereas sympathetic fibers innervate all areas of the heart. TRUE/FALSE

TRUE.

Norepinephrine acts on which receptors?

Norepi released by sympathetic fibers interacts with beta-1 receptors on cardiac muscle cells, leading to increased contractility by promoting increased Ca+ influx with each action potential.

What does acetylcholine have in common with parasympathetic fibers?

These fibers release acetylcholine and are more selective in their innervation.
Acetylcholine increases membrane permeability of the SA node to K+, therby hyperpolarizing the cell membranes and rendering them less susceptible to depolarization.